So , when i first bought my pre-built pc ( roughly 1.5 years ago ) it already have 2x2GB Transcend Ram sticks inside , i was a total newbie back then thus the pre-build pc , now that i have a "clue " of whats going on regarding computers i upgraded to 2x4GB Corsair XMS3 kit , my question is , can i just add the 2 sticks that came with the pc before i upgraded? giving me a total of 12GB of ram? Or it has to be of the same manufacturer?
Shouldn't be any problem mate, even if the Corsair sticks have higher clock speeds they'll automatically run at the same speed of the ram you already had installed, give it a try.
Hmm , by runing at lower clock speed won't the transcend then kinda bottleneck the Corsair ones? Won't my pc run slower?
Not really worth the time or hassle of running the older (and as you say, slower ram) if you not going to make use of it. Are you running out of ram with the 8gb you just installed? More isn’t always better, best to keep it simple. Chances are, you’ll never notice the difference in speed if you do mix and match. As suggested above, do before and after tests.